The overall goal of this project is to determine the causes of follicular atresia in the cycling rat. Anti-testosterone antiserum will be administered to test the hypothesis that accumulation of androgen within the follicle is the immediate cause of atresia. To determine if the LH surge promotes atresia, and prior exposure to FSH prevents atresia, the components of the periovulatory surge of gonadotropins will be dissociated. Porcine follicular fluid ("inhibin") will be used to attenuate the FSH surge; exogenous FSH and LH will be administered to "advance" or augment the endogenous gonadotropin surges. The effect of these treatments on the number and viability of small antral follicles (those follicles particularly prone to atresia), will be examined by histological methods. A time course will be established for the sequence of morphological events associated with atresia in these follicles. Small antral follicles will be isolated and placed in tissue culture to determine if exposure to the LH surge stimulates androgen production, and exposure to the FSH surge stimulates aromatase enzyme activity.